240 VERTEBRATE ANIMALS. 



of considerable commercial importance, as it furnishes the 

 " tortoise-shell " of trade, so largely used in various kinds of 

 ornamental work. 



FIG. 119. The Hawk-billed Turtle (CJwlonia imbricata). (After Bell.) 



The Sea-tortoises or Turtles have the carapace much flat- 

 tened, the legs of unequal length, in the form of solid fins or 

 oars, the toes being conjoined, and hardly distinct from one 

 another. 



The Marsh, Pond, and River Tortoises are generally fur- 

 nished with webbed feet, and lead an amphibious, semi-aquatic 

 existence. The so-called " Soft Tortoises " (Trionycidce] be- 

 long here, and are distinguished by the imperfect condition 

 of the carapace, which is simply covered with a leathery skin. 

 A good example is the Soft-shelled Turtle (T.ferox) of the 

 Southern States. Here also belong the Snapping-turtles, so 

 well known in the person of the common American species 

 (Chetydra serpentina), and the Terrapins (Emydidce), of 

 which many forms are found in all parts of the United States. 

 In the curious little Box-tortoise ( Cistudo Virgined) the plas- 

 tron is composed of two movable portions which can be 

 brought into accurate apposition with the carapace, thus com- 

 pletely protecting the animal within. 



The Land Tortoises have short legs of nearly equal length, 

 the toes little distinct, and united into a sort of stump, with 

 indistinct, horny claws. Good examples of this group are the 



